Stent with offset cell geometry

ABSTRACT

A stent defining a longitudinal axis is disclosed. A plurality of circumferential support structures are spaced-apart along the longitudinal axis. At least some of the circumferential support structures are interconnected by connection members that extend generally in a circumferential direction.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention pertains to implants for use in intraluminalapplications. More particularly, this invention pertains to stents foruse in vascular applications.

[0003] 2. Description of the Prior Art

[0004] Stents are widely used for supporting a lumen structure in apatient's body. For example, stents may be used to maintain patency of acoronary artery, other blood vessel or other body lumen.

[0005] Commonly, stents are metal, tubular structures. Stents are passedthrough the body lumen in a collapsed state. At the point of anobstruction or other deployment site in a body lumen, the stent isexpanded to an expanded diameter to support the lumen at the deploymentsite.

[0006] In certain designs, stents are open-celled tubes that areexpanded by inflatable balloons at the deployment site. This type ofstent is often referred to as a “balloon expandable” stent and is oftenmade of a plastically deformable material such as stainless steel. Otherstents are so-called “self-expanding” stents. Self-expanding stents donot use balloons to cause the expansion of the stent. An example of aself-expanding stent is a tube (e.g., a coil tube or an open-cell tube)made of an elastically deformable material. Elastically deformableself-expanding stents are typically secured to a stent delivery deviceunder tension in a collapsed state. At the deployment site, the stent isreleased so that internal tension within the stent causes the stent toself-expand to its enlarged diameter. This type of stent is often madeof a “super-elastic” material such as nitinol. Other self-expandingstents are made of so-called shape-memory metals. Such shape-memorystents experience a phase change at the elevated temperature of thehuman body. The phase change results in expansion from a collapsed stateto an enlarged state.

SUMMARY OF THE INVENTION

[0007] One embodiment of the present invention relates to a stent havinga longitudinal axis. A plurality of circumferential support structuresare spaced-apart along the longitudinal axis. At least some of thecircumferential support structures are interconnected by connectionmembers that extend generally in a circumferential direction.

[0008] A variety of advantages of the invention will be set forth inpart in the description that follows, and in part will be apparent fromthe description, or may be learned by practicing the invention. It is tobe understood that both the foregoing general description and thefollowing detailed description are exemplary and explanatory only andare not restricted.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a plan view of a first embodiment of a stent accordingto the present invention as it would appear if it were longitudinallysplit and laid out flat.

[0010]FIG. 2 is the view of FIG. 1 following expansion of the stent.

[0011]FIG. 3 is a partial plan view of a tapered-strut stent accordingto the present invention as it would appear if it were longitudinallysplit and laid out flat.

[0012]FIG. 4 is a partial plan view of another embodiment of a stentaccording to the present invention as it would appear if it werelongitudinally split and laid out flat.

[0013]FIG. 5 is a partial plan view of another embodiment of a stentaccording to the present invention as it would appear if it werelongitudinally split and laid out flat.

[0014]FIG. 6 is an enlarged partial view of the stent of FIG. 1.

[0015]FIG. 7 is a partial plan view of another embodiment of a stentaccording to the present invention, as it would appear if it werelongitudinally split and laid out flat.

[0016]FIG. 8 is a plan view of another embodiment of a stent accordingto the present invention, as it would appear if it were longitudinallysplit and laid out flat.

[0017]FIG. 9 is a plan view of another embodiment of a stent accordingto the present invention, as it would appear if it were longitudinallysplit and laid out flat.

[0018] While the invention is amenable to various modifications andalternative forms, the specifics thereof have been shown by way ofexample in the drawings and will be described in detail below. It is tobe understood, however, that the intention is not to limit the inventionto the particular embodiments described. On the contrary, the inventionis intended to cover all modifications, equivalents and alternativesfalling within the scope of the invention as defined by the appendedclaims.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

[0019] Referring now to the several drawing figures in which identicalelements are numbered identically, a description of the preferredembodiment of the present invention will now be provided. In thefollowing detailed description, references are made to the accompanyingdrawings that depict various embodiments in which the invention may bepracticed. It is to be understood that other embodiments may beutilized, and structural and functional changes may be made withoutdeparting from the scope of the present invention. Further, each of thefeatures disclosed herein can be considered stand-alone inventivefeatures or features that have inventive aspects when considered incombination with one another.

[0020]FIG. 1 illustrates a stent 10, shown longitudinally split and laidflat, having an un-deployed or reduced circumference C_(r) and anun-deployed length L. FIG. 6 is an enlarged partial view of FIG. 1 tobetter illustrate a strut geometry as will be described.

[0021] The stent 10 is a reticulated, hollow tube. The stent 10 may beexpanded from the reduced circumference C_(r) to an expanded or enlargedcircumference C_(e). FIG. 2 is a view illustrating the expanded stent 10as it would appear if longitudinally split and laid flat. The enlargedcircumference C_(e) is shown in FIG. 2.

[0022] The material of the stent 10 defines a plurality ofcircumferential support structures 12 spaced apart along thelongitudinal axis, X-X of the stent 10. The phrase “circumferentialsupport structures” will be understood to include structures that extendgenerally about the circumference of the stent 10. The supportstructures 12 are formed by longitudinal struts 14. In one embodiment,the struts 14 have uniform cross-sectional dimensions throughout theirlength. Adjacent struts 14 within a support structure 12 are connectedat apex portions 18 to form an undulating pattern that extends about thecircumference of the stent 10. As used herein, “apex portion” isintended to mean the region where two struts 14 are joined. The apexportions 18 can be semi-circular, arcuate, pointed, square, oval, or anyother shape. Adjacent support structures 12 are joined bycircumferential connecting struts 16 joining apex portions 18. Thephrase “circumferential connecting struts” or “circumferentialconnecting members” will be understood to mean struts or members thatinterconnect adjacent circumferential support structures 12 and have aspacial component or vector that extends in a circumferential directionabout the stent 12. The struts 14, apex portions 18 and connectingstruts 16 form bounded areas, or cells 20, which are open as shown inFIG. 2 (i.e., extend through the wall thickness of the stent 10).

[0023] The struts 14 may all be the same length, or they may be ofdiffering length. In one embodiment, when some longer struts arepresent, the longer struts in adjacent support structuresinterconnected.

[0024] The stent 10 may be formed through any suitable means includinglaser or chemical milling. In such processes, a hollow cylindrical tubelaser cut or etched to remove material and form the open cells 20.

[0025] In the embodiment of FIG. 1, the struts 14 extend along thelongitudinal axis of the stent in the un-deployed orientation (FIGS. 1and 6). At least some of the apex portions 18 are configured such that,when the stent is in the un-deployed orientation, they overlap in theaxial/longitudinal direction. As used herein, “overlap” is intended tomean the apex portions 18 are directly in line circumferentially, or theapex portions 18 extend past each other such that the connecting strutjoining them is positioned at an angle relative to the circumference. Inthe embodiment illustrated in FIGS. 1 and 6, the overlapping apexportions 18 are directly in line circumferentially, and the connectingstruts 16 are substantially perpendicular to the struts 14. In theembodiment illustrated in FIG. 7, apex portions 118 extending past eachother are joined by angled connecting struts 416. The angled connectingstruts 416 extend at an oblique angle with respect to thecircumferential direction.

[0026] The embodiment of FIG. 3 includes longitudinal struts 114 thatare tapered, as disclosed in co-pending, commonly assigned, U.S. patentapplication Ser. No. 09/765,725, the entire disclosure of which isincorporated herein by reference. In the embodiment illustrated in FIG.3, circumferential support structures 112 are made up of pairs oftapered struts 114 alternating with single, non-tapered struts 113. Thetapered struts 114 are arranged such that their wide ends 115 areadjacent circumferential connecting struts 116 and their narrow ends 117are adjacent unconnected or free apex portions. In a further embodiment,the connecting struts 116 can connect only apex portions 118 joiningnarrow ends 117.

[0027] To increase the radiopacity of the stent, one or more of theconnecting struts can have a width greater than the width of thelongitudinal struts 14. In the embodiment illustrated in FIG. 4, allconnecting struts 216 are wide. Preferably, the connecting struts 216are at least 1.25, or 2, or 3, or 4, or 5, or 6, or 7 or 8 times as wideas the strut By way of example, the connecting struts might range from0.01 inch to 0.050 inches in width. In the embodiment illustrated inFIG. 5, wide connecting struts 216 are positioned between some of thesupport structures 12, and narrower connecting struts 16 are positionedbetween the remaining support structures 12. Incorporating both wideconnecting struts 216 and narrower connecting struts 16 in the stent canprovide a customized radiopacity.

[0028] In use, the stent 10 is advanced to a site in a lumen (e.g., anocclusion site in need of circumferential support) while in thecompressed orientation. The stent 10 is then expanded at the site. Thestent 10 may be expanded through any conventional means. For example,the stent 10 in the reduced diameter may be placed at the tip of aballoon catheter. At the site, the stent is expanded (e.g., throughexpansion of the balloon) thereby causing the stent to expand from thecompressed orientation to the deployed orientation. A preferred materialfor balloon expandable stents is stainless steel. For self-expandingstents, the stent 10 may be formed of a super-elastic or shape memorymaterial, such as nitinol, which is an alloy of nickel and titanium.

[0029] During expansion of the stent 10, the cells 20 open to aconfiguration as shown in FIG. 2. The expansion of the stent 10 istypically provided primarily through bending of the apex portions 18.

[0030] The stent 10 is highly flexible. To advance to a site, the axisX-X of the stent 10 bends to navigate through a curved lumen. Further,for placement at a curved site in a lumen, the stent 10 is preferablysufficiently flexible to retain a curved shape following expansion andto bend as the lumen bends over time. The stent 10, as described above,achieves these objections.

[0031] When bending on its axis X-X, the stent 10 tends to axiallycompress on the inside of the bend and axially expand on the outside ofthe bend. The present design permits such axial expansion andcontraction. The cell geometry results in a structure that is highlyflexible before and after radial expansion.

[0032] When the stent 10 is in the deployed orientation, as shown inFIG. 2, the apex portions 18 on adjacent support structures 12 areoffset. When the stent 10 flexes and bends, the apex portions 18 andcorresponding struts 14 on one support structure 12 do not come indirect contact with facing apex portions 18 and struts 14 on an adjacentsupport structure 12. This offset geometry provides increasedflexibility to the stent 10 and allows the stent 10 to better conform toa lumen such as a coronary vessel.

[0033] In one embodiment, as shown in FIG. 2, the distance of offset D₁provided by the connection member 16 is about one-half the distance D₂provided between the apex portions 18 (i.e., D₁=0.5D₂). Thus, adjacentcircumferential support structures 12 define waves that are “in-phase”with one another. This provides a greater longitudinal spacing (i.e., ina direction corresponding to the longitudinal axis of the stent) betweenthe peaks as compared to having the apexes being in direct opposition toone another.

[0034] Table 1 provides examples of stent diameters and examples ofoffset geometry based on the number of apex portions around thecircumference of the stent. It is to be understood that the dimensionsin Table 1 are exemplary only and are not intended to be limiting. Thedimensions are applicable to a stent in the expanded or deployedorientation. The stent dimensions will be selected based on the size andlocation of the lumen into which the stent is to be placed. This offsetgeometry allows for flexion of the stent without adjacent strutsdirectly impacting each other. The preferred geometry has the apexes ofstruts in one support structure in between the apexes of struts in theadjacent support structure. When the stent is flexed, the apexes pass byone another and do not impact, which allows for increased flexibility.TABLE 1 Preferred Offset: Distance between ½ distance between I.D. I.D.Number of apexes around apexes around Diameter Diameter Circumferenceapexes around Circumference Circumference (mm) (inch) (inch)Circumference (inch) (inch) 6.25 0.246 0.773 18 0.043 0.021 7.25 0.2850.897 18 0.050 0.025 8.25 0.325 1.020 18 0.057 0.028 9.25 0.364 1.144 180.064 0.032

[0035] Numerous modifications are possible. For example the stent 10 maybe lined with either an inner or outer sleeve (such as polyester fabricor ePTFE) for tissue growth.

[0036] Also, the stent may be coated with radiopaque coatings such asplatinum, gold, tungsten or tantalum. In addition to materialspreviously discussed, the stent may be formed of any one of a widevariety of previous known materials including, without limitation,MP35N, tantalum, platinum, gold, Elgiloy and Phynox.

[0037] While twenty support structures 12 are shown in FIGS. 1 and 2connected and spaced apart along the longitudinal axis of the stent, adifferent number could be so connected to vary the properties of thestent 10 as a designer may elect. Likewise, while each support structure12 in FIGS. 1 and 2 is shown as having 36 struts 14, the number ofstruts 14 could vary to adjust the properties of the stent. Also, whileeach support structure 12 is shown connected to an adjacent supportstructure 12 by 6 connecting struts 16, the number of connecting struts16 could vary. In one embodiment, the stent is made up of 20 supportstructures, 36 struts per support structure, 18 apex portions on eachside of each support structure, and 6 connecting struts joining everythird apex portion of adjacent support structures. Alternating thedirection of the connecting struts between support structures preventsuneven expansion angles between the struts and prevents twisting of thestent. For example, in FIG. 1, connecting struts 16 extend from one apexportion 18 down to another apex portion 18 between first and secondsupport structures, and extend up between the second and third supportstructures. This alternating pattern of connecting struts is morepronounced in the embodiment with angled connecting struts 416, shown inFIG. 7.

[0038] When forming the stent from shape memory metal such as nitinol,the stent can be laser cut from a nitinol tube. Thereafter, the stentcan be subjected to a shape-setting process in which the cut tube isexpanded on a mandrel and then heated. Multiple expansion and heatingcycles can be used to shape-set the stent to the final expandeddiameter.

[0039] In use, the finished stent can be mounted on a delivery catheter.As is conventionally known in the art, the stent can be held in acompressed orientation on the delivery catheter by a retractable sheath.As is also known in the art, the delivery catheter can be used toadvance the stent to a deployment location (e.g., a constricted regionof a vessel). At the deployment cite, the sheath is retracted therebyreleasing the stent. Once released, the stent self-expands to thedeployed diameter.

[0040]FIG. 8 shows another stent 510 that is another embodiment of thepresent invention. The stent 510 is shown in a configurationcorresponding to the stent when the stent has been initially fabricatedfrom a tube (i.e., before the stent has been compressed on a catheter).Similar to the previous embodiments, the stent is shown longitudinallysplit and laid flat for ease of explanation. The stent includes 10circumferential support structures CS1-CS10 spaced-apart along alongitudinal axis LA of the stent 510. Longitudinal struts 14 and apexportions 18 of the support structures CS1-CS10 define an undulatingpattern that extends about the circumference of the stent 510. Theundulating pattern defines a wave having a wavelength WL. Alternatingpairs of the adjacent support structures are interconnected bycircumferential connecting struts 16. For example, support structurepairs CS2 and CS3; CS4 and CS5; CS6 and CS7; and CS8 and CS9 areinterconnected by circumferential connecting struts 16. Struts 16interconnecting structure CS2 to structure CS3 and structure CS6 tostructure CS7 extend downwardly, and struts 16 interconnecting structureCS4 to structure CS5 and structure CS8 to structure CS9 extend upwardly.By alternating the direction of extension, uniform expansion isfacilitated.

[0041] Circumferential support structures CS1 and CS2; CS3 and CS4; CS5and CS6; CS7 and CS8; and CS9 and CS10 are not interconnected bycircumferential connecting struts. Instead, these pairs are integrallyconnected to one another.

[0042] Referring again to FIG. 8, the circumferential connecting struts16 function to offset the apexes 18 of adjacent circumferential supportstructures relative to one another so that the apexes do not oppose oneanother. By offsetting the apex portions that face toward one another,the tips are prevented from contacting one another when in the expandedstate thereby enhancing the stent's ability to conform to a lumen inwhich the stent is implanted. In the depicted embodiment, thecircumferential connecting struts 16 have a length equal to about oneand one half (i.e., 1.5) wavelengths WL. Preferably, the circumferentialstruts 16 have a length of at least one half (i.e., 0.5) the wavelengthWL. The integrally connected pairs of circumferential support structureshave apex portions 18 that oppose one another.

[0043]FIG. 9 shows a stent 610 that is another embodiment of the presentinvention. The stent 610 is shown in a configuration corresponding tothe stent when the stent has been initially fabricated from a tube(i.e., before the stent has been compressed on a catheter). Similar tothe previous embodiments, the stent is shown longitudinally split andlaid flat for ease of explanation. The stent includes 10 circumferentialsupport structures CS1-CS10 spaced-apart along a longitudinal axis LA ofthe stent 610. Longitudinal struts 14 and apex portions 18 of thesupport structures CS1-CS10 define an undulating pattern that extendsabout the circumference of the stent 510. Support structure pairs CS2and CS3; CS3 and CS4; CS7 and CS8; and CS8 and CS9 are interconnected bycircumferential connecting members 16. The remaining support structurepairs (i.e., pairs CS1 and CS2; CS4 and CS5; CS5 and CS6; CS6 and CS7;and CS9 and CS10) are interconnected by integrally.

[0044] In the embodiments of FIGS. 8 and 9, the circumferentialconnecting struts 16 are generally perpendicularly aligned relative tothe apex portions 18. In other embodiments, the circumferentialconnecting struts 16 could be angled similar to the struts 416 of FIG.7. In embodiments where the apex portions 18 are not longitudinallyoverlapped, the circumferential connecting struts could be angled in theopposite direction as compared to the struts 416 of FIG. 7.

[0045] While a preferred use for the inventive features disclosed inFIGS. 1-9 is in a self-expanding stent, the features also have benefitswhen used with non-self-expanding stents (e.g., balloon expandablestents made of a material such as stainless steel). Also, while FIGS.1-9 illustrate a preferred geometry for practicing the presentinvention, the technique for avoiding opposing longitudinal memberscoming in direct contact by varying the offset positions of the strutsand apex positions in a stent is also applicable to stents having othergeometries, shapes, or strut patterns.

[0046] From the foregoing, the present invention has been shown in apreferred embodiment. Modifications and equivalents are intended to beincluded within the scope of the appended claims.

What is claimed is:
 1. A stent comprising: a stent body expandablebetween an un-deployed orientation and a deployed orientation, the stentbody having a longitudinal axis extending between first and second openends; the stent body having a plurality of adjacent circumferentialsupport structures, the circumferential support structures beingspaced-apart along the longitudinal axis; each support structureincluding longitudinal struts interconnected at apex portions, thelongitudinal struts and apex portions defining an undulating pattern, atleast some of the apex portions of adjacent circumferential supportstructures being configured to longitudinally overlap one another whenin the un-deployed configuration; a plurality of circumferentialconnecting struts interconnecting at least some of the adjacentcircumferential support structures, the circumferential connectingstruts extending between the apex portions that overlap one another. 2.The stent of claim 1 wherein in the deployed orientation, adjacentcircumferential support structures are offset such that the apexportions on one side of a support structure are positioned intermediatethe apex portions on a facing side of an adjacent support structure. 3.The stent of claim 1 wherein at least some of the circumferentialconnecting struts have a width greater than a width of the longitudinalstruts.
 4. The stent of claim 1 wherein at least some of thecircumferential connecting struts have a width at least twice as greatas a width of the longitudinal struts.
 5. The stent of claim 1 whereinat least some of the longitudinal struts have widths that taper as theat least some longitudinal struts extend along the stent bodylongitudinal axis.
 6. The stent of claim 5 wherein each circumferentialsupport structure comprises pairs of tapered struts alternating withsingle, non-tapered struts.
 7. The stent of claim 6 wherein the pairs oftapered struts are longer than the non-tapered struts.
 8. The stent ofclaim 7 wherein the pairs of longer tapered struts are interconnected bythe circumferential connecting struts.
 9. The stent of claim 1 whereinthe circumferential connecting struts joining first and second adjacentsupport structures extend in a first direction and the circumferentialconnecting struts joining second and third support structures extend ina second direction opposite the first direction.
 10. The stent of claim1 wherein some of the longitudinal struts are longer than otherlongitudinal struts, and wherein the longer longitudinal struts providethe longitudinal overlap at the apex portions.
 11. The stent of claim 1wherein the circumferential connecting struts connecting the apexportions are angled with respect to a circumferential direction.
 12. Thestent of claim 1 wherein the undulating pattern defines a wavelength,and wherein the circumferential connecting members are at least one halfthe length of the wavelength.
 13. The stent of claim 1, wherein thecircumferential connecting members are located between only some of theadjacent pairs of circumferential support structures.
 14. The stent ofclaim 13, wherein some adjacent pairs of circumferential supportstructures have apex portions that oppose one another, and otheradjacent pairs of circumferential support structures have apex portionsthat are offset from one another.
 15. The stent of claim 13, whereinonly alternating pairs of circumferential support structures areinterconnected by the circumferential support structures.
 16. The stentof claim 13, wherein three consecutive circumferential supportstructures are interconnected by the circumferential connecting members.17. A stent comprising: a stent body expandable between an un-deployedorientation and a deployed orientation, the stent body having alongitudinal axis extending between first and second open ends; thestent body having a plurality of adjacent circumferential supportstructures, the circumferential support structures being spaced-apartalong the longitudinal axis; each support structure includinglongitudinal struts interconnected at apex portions, the longitudinalstruts and apex portions defining an undulating pattern; and a pluralityof circumferential connecting struts interconnecting at least some ofthe adjacent circumferential support structures, the circumferentialconnecting struts extending between the apex portions of adjacentcircumferential support structures, at least some of the circumferentialconnecting struts having a width greater than a width of thelongitudinal struts.
 18. The stent of claim 17 wherein at least some ofthe circumferential connecting struts have a width at least twice asgreat as the width of the longitudinal struts.
 19. A stent comprising: astent body expandable between an un-deployed orientation and a deployedorientation, the stent body having a longitudinal axis extending betweenfirst and second open ends; the stent body having a plurality ofadjacent circumferential support structures, the circumferential supportstructures being spaced-apart along the longitudinal axis; each supportstructure including longitudinal struts interconnected at apex portions,the longitudinal struts and apex portions defining an undulatingpattern; and a plurality of circumferential connecting strutsinterconnecting only some of the adjacent circumferential supportstructures, the circumferential connecting struts extending between theapex portions of adjacent circumferential support structures, whereinsome pairs of adjacent circumferential support structures have apexportions that oppose one another, and other pairs of adjacent supportstructures have apex portions that are offset by the circumferentialconnecting struts.
 20. The stent of claim 19, wherein only alternatingpairs of circumferential support structures are interconnected by thecircumferential support structures.